Kulkarni R N, Wang Z L, Akinsanya K O, Bennet W M, Wang R M, Smith D M, Ghatei M A, Byfield P G, Bloom S R
Francis Fraser Laboratories, Department of Metabolic Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, London, United Kingdom.
Endocrinology. 1995 Nov;136(11):5155-64. doi: 10.1210/endo.136.11.7588254.
TRH immunoreactivity has been detected in the pancreas of man and rat and localized to the islets of Langerhans. We studied the effect of synthetic TRH and the related tripeptide pyroglutamyl-phenylalanyl-proline amide (EFP) on isolated perifused rat islets and the glucose-responsive clonal cell lines HIT-T15 and RIN5AH. TRH at 10 nM potentiated [0.5 +/- 0.1 (control) vs. 0.8 +/- 0.1 (TRH) pmol/10(6) cells per 120 min; mean +/- SEM; n = 6; P < 0.001; n = 15], whereas EFP from 1 nM upwards suppressed glucose-stimulated insulin secretion [0.8 +/- 0.1 (control) vs. 0.5 +/- 0.1 (EFP) pmol/10(6) cells per 120 min; P < 0.001; n = 12) in the cell lines. Further, EFP reversed TRH-stimulated insulin release. Similar responses were observed in perifused isolated rat islets at the tested dose of 1 microM. Gel permeation chromatography of rat adult and neonatal whole pancreas, isolated islets, and HIT cell extracts demonstrated the elution of total TRH-like immunoreactivity (t-TRH-LI) in the same position as synthetic TRH. Cation exchange analysis of the t-TRH-LI from rat adult pancreas and HIT cell extracts showed that neutral TRH-like peptides corresponding to synthetic EFP were also present. Reverse-phase fast protein liquid chromatographic analysis of t-TRH-LI in the unbound fraction of these extracts subjected to anion exchange columns, also demonstrated peaks corresponding to synthetic EFP. We conclude that TRH potentiates, whereas EFP inhibits, glucose-stimulated insulin release in isolated perifused islets and the cell lines. In addition, EFP reversed the stimulatory effect of TRH. The presence of EFP-LI in rat adult and neonatal pancreas and HIT cell extracts suggests it may contribute in the modulation of pancreatic endocrine function.
已在人和大鼠的胰腺中检测到促甲状腺激素释放激素（TRH）免疫反应性，并定位于胰岛。我们研究了合成TRH和相关三肽焦谷氨酰 - 苯丙氨酰 - 脯氨酸酰胺（EFP）对分离的灌注大鼠胰岛以及葡萄糖反应性克隆细胞系HIT - T15和RIN5AH的影响。10 nM的TRH增强了胰岛素分泌[每120分钟每10⁶个细胞0.5±0.1（对照）对0.8±0.1（TRH）pmol；平均值±标准误；n = 6；P < 0.001；n = 15]，而1 nM及以上的EFP抑制了细胞系中葡萄糖刺激的胰岛素分泌[每120分钟每10⁶个细胞0.8±0.1（对照）对0.5±0.1（EFP）pmol；P < 0.001；n = 12]。此外，EFP逆转了TRH刺激的胰岛素释放。在1 microM的测试剂量下，在灌注的分离大鼠胰岛中观察到类似的反应。对成年和新生大鼠全胰腺、分离的胰岛以及HIT细胞提取物进行凝胶渗透色谱分析，结果显示总TRH样免疫反应性（t - TRH - LI）的洗脱位置与合成TRH相同。对成年大鼠胰腺和HIT细胞提取物中的t - TRH - LI进行阳离子交换分析表明，也存在与合成EFP相对应的中性TRH样肽。对这些提取物经阴离子交换柱后的未结合部分中的t - TRH - LI进行反相快速蛋白质液相色谱分析，也显示出与合成EFP相对应的峰。我们得出结论，TRH增强而EFP抑制分离的灌注胰岛和细胞系中葡萄糖刺激的胰岛素释放。此外，EFP逆转了TRH的刺激作用。在成年和新生大鼠胰腺以及HIT细胞提取物中存在EFP免疫反应性，表明它可能参与胰腺内分泌功能的调节。
